Our Galaxy, the Milky Way Galaxy Examination lecture notes

Flashcards covering vocabulary terms from the lecture notes on Our Galaxy, the Milky Way Galaxy, galactic structures, dark matter, the interstellar medium, star populations, star clusters, nebulae, galactic properties, galactic evolution, active galaxies, gamma-ray bursts, and cosmology.

Galaxy

A collection of billions of star systems held together by gravity.

Milky Way Galaxy

The galaxy containing our Solar System, composed of roughly one hundred billion star systems arranged in a flat disk with spiral arms.

Galactic Disk

The flat, disk-shaped region of a galaxy where most of the stars and gas are concentrated.

Galactic Bulge

A collection of stars arranged into a more rounded shape near the center of our Milky Way Galaxy.

Galactic Halo

A region around the galactic disk (above and below the galactic disk) where some stars can be found.

Spiral Density Waves

Propagating disturbances throughout all the stars that together form our Milky Way Galaxy, which contribute to the changing structure of the spiral arms of the Milky Way Galaxy.

Galactic Year

The time it takes our Solar System to complete one orbit around the center of our Milky Way Galaxy; between two hundred million years and two hundred and fifty million years.

Galactic Dynamics

The study of the structure and the evolution of galaxies.

Galactic Dynamicists

Astrophysicists who study the structure and the evolution of galaxies.

Supermassive Black Hole

A black hole with a mass at least in the millions of solar masses, located at the center of every major galaxy in the universe.

Rotation Curve

A graph of the orbital speed of stars around the center of a galaxy as a function of their distance from the center of the galaxy.

Dark Matter

Mysterious mass that does not interact with any photons at all and composes roughly ninety percent of the mass of all galaxies in the universe.

Dark Matter Halo

An enormous sphere surrounding all the star systems of a galaxy, over which roughly ninety percent of the mass of our Milky Way Galaxy is distributed.

Normal Matter

The remaining roughly ten percent of the mass of the universe that is composed of atoms.

MACHOs

Massive astrophysical compact halo objects; brown dwarf stars in the galactic halo surrounding all the other stars of a galaxy.

WIMPs

Weakly interacting massive particles; hypothetical supersymmetric particles claimed as the composition of dark matter.

Interstellar Medium (ISM)

Very diffuse gas that fills outer space and is concentrated within the galactic disk, filling the space between stars.

Diffuse Nebula

A region of the interstellar medium that is more dense than average.

Population I Stars

Stars within the galactic disk and are comparatively young.

Population II Stars

Stars within the galactic halo and are comparatively old.

Metals

All the atoms on the Periodic Table of Elements besides hydrogen or helium.

Metallicity

The fraction (percentage) of its normal (atomic) mass that is composed of metals (all atoms besides hydrogen and helium).

Population III Stars

The very first generation of stars born in the entire universe that had zero metallicity.

Open Star Clusters

Star clusters within the galactic disk that are composed of Population I stars.

Globular Star Clusters

Star clusters within the galactic halo (outside of the galactic disk) that are composed of Population II stars.

Embedded Star Clusters

Particularly young open star clusters that are often still embedded within the diffuse nebula from which they formed.

OB Associations

Star clusters with a significant number of O-type and B-type stars.

Superbubble

Spherical region that surrounds every OB association, where the interstellar medium is less dense than average.

Absorption Nebulae

Diffuse nebulae that tend to appear black in color, since they absorb photons.

Emission Nebulae

Diffuse nebulae with stars within them that were recently born from the gases within the nebula itself and emit photons.

Reflection Nebulae

Diffuse nebulae that tend to appear blue in color, since shorter wavelengths of light are more preferentially scattered than longer wavelengths of light.

Reddening

The effect of shorter-wavelength blue light being preferentially scattered with the longer-wavelength red light as light traverses interstellar space.

Extinction

The total amount of light that has been either scattered or absorbed by the interstellar medium.

Satellite Galaxies

Small galaxies that orbit our Milky Way Galaxy.

Local Galactic Group

The collection of several dozen galaxies that together define our galactic neighborhood.

Variable Star

Star that has a luminosity (absolute magnitude or intrinsic brightness) that varies significantly.

Period-Luminosity Relations

Equations relating the average luminosity of variable stars with their pulsation period.

Great Debate

The debate over the true nature of spiral nebulae to be island universes of billions of stars, between astronomers Harlow Shapley and Heber Curtis.

Elliptical Galaxies

One of the main types of galaxies in our universe that are more round in structure (shape).

Tully-Fisher Relation

An equation that correlates the orbital speed of stars within a spiral-disk galaxy to the luminosity of the spiral-disk galaxy, to determine distance.

Faber-Jackson Relation

An equation that correlates the velocity dispersion of stars within an elliptical galaxy to the luminosity of the elliptical galaxy, to determine distance.

Galactic Groups

Organizations composed of several dozen galaxies.

Galactic Clusters

Organizations composed of hundreds of large major galaxies.

Intergalactic Medium

Diffuse gas that fills the space between galaxies within galactic clusters.

Intracluster Medium

Diffuse gas that fills the space within a galactic cluster.

Galactic Superclusters

Organizations that galactic groups and galactic clusters are clumped into.

Cosmic Voids

Enormous regions between galactic superclusters that are nearly empty of galaxies.

Cosmic Filaments

Colossal organizations galactic superclusters are clumped into, each containing between a few hundred thousand and a few million galaxies.

Cosmic Supervoids

Colossal regions between cosmic filaments that are nearly completely empty of galaxies.

End of Greatness

Cosmologists call the homogeneous (smooth) distribution of mass at these titanic size scales.

Type Ia Supernova

A thermonuclear detonation that obliterates an entire white dwarf in a cataclysmic explosion that liberates energy in the billions of solar luminosities.

Standard Candles

A light source with a known luminosity (power output) that we may combine with its apparent brightness to determine its distance.

Hubble Sequence

Classification of galaxies based on the Hubble classification diagram into elliptical galaxies from E0 through E7, and spiral-disk galaxies. Unbarred spirals from Sa through Sc, and barred spirals from SBa through SBc.

Protogalactic Cloud

An enormous cloud of gas millions of light-years across.

density-angular-momentum theory of galactic birth

A galaxy is born with a particular Hubble type along the Hubble sequence depending on the density and the angular momentum of the protogalactic cloud from which it formed.

collision-merger theory of galactic birth

All galaxies are initially born spiral-disk galaxies, forming from the collision and merger of several small protogalactic clouds; large elliptical galaxies result from the collision and merger of two large spiral-disk galaxies.

Milkdromeda Galaxy

The elliptical galaxy that will be born in roughly five billion years as the merger of our Milky Way Galaxy and the Andromeda Galaxy.

Starburst Galaxy

A large irregular galaxy with much more active star formation than even spiral-disk galaxies.

Active Galaxies

Distant galaxies that contain incredibly luminous centers,

Active Galactic Nuclei (AGNs)

The luminous centers of active galaxies.

Seyfert Galaxies

Active and distant galaxies that are not as active and not as distant as quasi-stellar objects.

Quasi-Stellar Objects (QSOs)

Also referred to as simply quasars, the most active and the most distant galaxies in the observable universe.

Gamma-ray Bursts (GRBs)

Bursts of gamma-rays that come roughly equally from all directions in the sky, from extremely distant galaxies.

Hypergiant Stars

Resulting from the Population III stars being born as very high-mass stars with masses roughly equal to the Eddington limit; swelled to become larger and more luminous than even supergiant stars.

Hypernova

The explosion of hypergiant stars with significantly greater luminosity than even a supernova.

Hawking Radiation

The stream of real particles radiating away from an isolated black hole as the black hole loses mass and therefore energy.

Hawking Temperature

The temperature association with Hawking radiation.

Hawking Entropy

Thermodynamic variable related to temperature and energy, entropy of an isolated black hole.

Evaporating Black Holes

Isolated black holes that loses mass and has a shrinking event horizon as it radiates Hawking radiation.

Exploding Black Holes

Evaporating black holes that explode with nearly infinite luminosity, at the very end of their lives.

Primordial Black Holes

Microscopic black holes with an event horizon roughly the size of the nucleus of an atom that could have been born in the fires of the Big Bang.

Cosmology

The study of the entire universe, the universe itself.

Olbers Paradox

Why is the sky dark at night?

Observable Universe

The finite part of the universe that we are only permitted to observe, constrain by the finite age of the universe and the finite speed limit of the universe.

Cosmic Horizon

The spherical edge of our own observable universe.

Big Bang

Beginning of our four-dimensional spacetime, and this single event that began our four-dimensional spacetime had infinite spacetime curvature.

General Theory of Relativity

Einstein's theory that reveals that our four-dimensional spacetime actually had a beginning at a finite time in the past, Einstein doubted for the beginning the three cosmic solutions

Big Crunch

Spacetime would end with an opposite of the Big Bang.

Closed Geometry

Density of mass throughout the universe is greater than the critical cosmic density,then the cosmic geometry of the universe is closed (sphere, ellipsoid geometries).

Open Geometry

Density of mass throughout the universe is less than this critical cosmic density, then the cosmic geometry of the universe is open (hyperboloid geometry).

Flat Geometry

Density of mass throughout the universe is exactly equal to the certain critical cosmic density, then the cosmic geometry of the universe is flat (Euclidean geometry).

Hubble Law

The universe is expanding. Hubble discovered that the light from all galaxies beyond our Local Galactic Group is redshifted, revealing that all galaxies beyond our Local Galactic Group are moving away from us = v=H0 d.

Cosmological Constant

A fudge factor into his General Theory of Relativity, which he called that Einstein introduced due to the doubts the universe actually had had a true beginning - Big Bang.

Cosmological Redshift

Stretching of spacetime carries galaxies away from us, there are redshifts caused by the stretching of the wavelength of light as it journeys from distant galaxies toward us.

Hubble Constant

The Hubble law stating v=H0 d equal to roughly seventy kilometers per second per megaparsec.

Hot Big Bang model of cosmology

As the universe expands, the early universe was hotter than the present universe, as the Big Bang will became cooler and cooler as it expands.

Strong, Electromagnetism, Weaker, Gravitational

Four fundamental forces (Listed in the correct order from strongest to weakest).

electroweak force, Relativistic Quantum Electroflavodynamics

At incredibly hot temperatures, the electromagnetic force and the weak nuclear force unify into a single force that they called that at a temperature of roughly three quadrillion kelvins unification.

Higgs-Englert particle

At 3 trillion kelvins, Relativistic Quantum Electroflavodynamics the electroweak force divorces itself into the electromagnetic force and the weak nuclear force through a spontaneously broken symmetry involving something.

LHC - Large Hadron Collider in Europe

achieved electroweak unification with high power electromagnets, In the year 2012 caused particle collisions energetically violent enough to finally synthesize the Higgs-Englert particle.

GUTs .grand unification theories

After the discovery of Electroweak unification, theoretical physics that unifies the strong nuclear force with the electroweak force.

Supersymmetric Relativistic Quantum Field Theory

Every particle of matter or antimatter in the universe, there is a corresponding supersymmetric particle = popular grand unification theory.

super unification theories SUTs/ Theories OF Everything TOEs

Even hotter unification with the grand-unified force unifies with the gravitational force.

Brane theory

String theory, membranes M theory such as Matrix theory, Mystery..etc all compose a super unification theory /TOE to compose all particles and even curvature of spacetime being all composed of vibrating branes membranes fantastically tiny, very very small.

Planck Epoch

Time zero , from a time of roughly 5×10–44 seconds, roughly fifty quadrillionths of one quadrillionth of one quadrillionth of one second after God created the universe temperature of the universe cooled from infinity down to roughly one hundred nonillion kelvins! there was only a single fundamental force in the entire universe.

GUT Epoch

Time of roughly 5×10–44 seconds to a time of roughly 10–36 seconds temperature of the universe cooled from roughly 1032 kelvins down to 1029 kelvins! there were two fundamental forces in the entire universe: grand-unified force and the gravitational force.

Electroweak

EpochTime of roughly 10–36 seconds to a time of roughly 10–11 seconds and the temperature of the universe cooled from roughly 1029 kelvins down to 3×1015 there were three fundamental forces in the entire universe(strongNuclearforce / electroWeaker Gravitational force..)

Particle Epoch

Time/temperature = 10^-11 , to one hundredth of one second/ 10^11 kelvins where quarks/ leptons and gluons with their combination made protons and neutrons to make normal matter.

Nucleosynthesis Epoch

This time was in effect for approximaely, 0.01 one hundredth second to 3 minutes / one Billion Kelvins where protons and neutrons with chemical composition should be roughly ~75% H/ 25% He..Cosmic neutrino bckd generated.

Recombination Epoch

Time Temperature After ~ after Big Bang : 300.000-400.000 years / 3240 -> 2710k. Electrons to make neutral H / He atons created. Cosmic photons Bckgrnd generate.